1 . Field of the Invention
The invention relates to a method for the optimization of joint arthroplasty component design, and more particularly to a method for the optimization of shoulder arthroplasty component design through the use of computed tomography scan data from arthritic shoulders.
2 . Description of the Related Art
Various prostheses for the replacement of the shoulder joint are known. In one example shoulder prosthesis, the upper portion of the humerus is replaced by a humeral component including (i) a stem that extends into a bore formed within the humerus and (ii) a generally hemispherical head portion that is connected to the stem. The hemispherical head of the humeral component articulates with a complementary concave section of a glenoid component mounted within the glenoid cavity of the scapula. This type of shoulder prosthesis may be called a “primary” or “total” prosthesis. In another example shoulder prosthesis, often called a “reverse” or “inverted” prosthesis, the glenoid component includes a convex section that articulates with a complementary concave section of the head of the humeral component.
One alternative to total shoulder replacement is referred to as shoulder hemiarthroplasty. In one version of this procedure, the humeral head is replaced with a generally hemispherical head that may or may not include a connected stem. The glenoid cavity of the scapula is not replaced with a glenoid component, but may be refinished in a way that gives it a smooth surface and a shape which matches the generally hemispherical replacement head. Another version of this procedure can use a glenoid component with resurfacing of the humeral head.
Several deficiencies have been found in currently available shoulder arthroplasty systems including glenoid sizes (primary and reverse) and humeral sizes that are not based on the anatomic distribution. In addition, the advent of reverse arthroplasty for the treatment of proximal humerus fractures has also changed the requirements for an appropriate fracture stem. Specific design features are necessary to make the fracture stem appropriate for hemiarthroplasty and reverse arthroplasty use. Although resurfacing of the humerus has become popular, the designs are not based on an anatomic distribution. The instrumentation that is currently available is inadequate and may lead to significant malposition in version and inclination.
Prior magnetic resonance imaging and cadaveric studies of glenohumeral anatomy have been performed on shoulders without arthritis (lannotti et al., “The normal glenohumeral relationships. An anatomical study of one hundred and forty shoulders”, J Bone Joint Surg Am. 1992; 74:491-500; Hertel et al, “Geometry of the proximal humerus and implications for prosthetic design”, J Shoulder Elbow Surg., July/August 2002, pp. 331-338; and Boileau et al., “The Three-Dimensional Geometry Of The Proximal Humerus—Implications For Surgical Technique And Prosthetic Design”, J Bone Joint Surg [Br], 1997; 79-B:857-865). However, in reality, shoulder arthroplasty is not performed on normal shoulders. Shoulder arthroplasty is performed in patients with arthritis in the setting of cartilage loss and usually associated bone loss. In order to make properly sized implants that will accommodate patients with arthritis, it is important to understand the anatomy of these patients.
Typically, the designing surgeon has used a system with three glenoid sizes. In one study, it was determined that the distribution of glenoid components used in total shoulder arthroplasty was as follows: 4% large, 40% medium, and 56% small. One can see that based on component use, the sizing of these implants is not optimal. If glenoid component sizes are not optimal, there may be issues related to perforation of the glenoid by fasteners used in attaching the glenoid component to the scapula. In addition, certain components may be too large for smaller patients resulting in component overhang and potentially leading to violation of important neurovascular structures. Thus, it could be hypothesized that the preference for small glenoid components may result from the desire to avoid glenoid perforation and/or avoid component overhang. However, larger glenoid components can lead to a better fitting prosthesis and greater stability.
Thus, there exists a need for a method for the optimization of joint arthroplasty component design, and in particular, there exists a need for a method for the optimization of shoulder arthroplasty component design.